Huh, silly Dryad. You'd think that cleansing all corruption would trigger a special event, but nooooooooo! TRY HARDER, MAGGOT. As a theory, i think the devs made it so because removing all corruption post-wall is almost impossible. They wouldn't want people to miss out on things that happen like that.
Also, breaking news. I have solo'd Destroyer, and if i can, so can everyone else! It just requires top-notch gear. So yeah, not really breaking news after all. Still much harder than EoW with pre-wall equivalent gear, though. Also, guns are very ineffective against it when compared to, say, repeater with unholy arrows. Meteor shots could somewhat even that balance, but the fact is that they can score a max of 2 hits (for a max of what, 32 damage per hit?), while unholy arrows can hit 5 times for up to 47 DAMAGE PER HIT (with hallowed repeater). Although the megashark shoots 3 times as fast, the potential damage of an unholy arrow is more than 3 times as large. Plus, the higher damage lends itself better to the high defense of the big-ass metal worm. If you factor in defense, unholy arrows can potentially deal 4.7 times as much damage as meteor shots, WHICH LEADS TO 2/3rds higher DPS, provided that all shots hit as many body segments as they can. So it's well worth using them. Also, flamethrower deals superb damage too.
Today's useless ramble has been brought to you by Boredom(tm).